Explosion-proof switch assembly



June 4, 1957 I A l. APPLETON 2,794,891

EXPLOSION-PROOF SWITCH ASSEMBLY Filed June 4. 1954 2 Sheets-Sheet 1 INVENTOR.

I BY .Z Wsfon June 4, 1957 A. I. APPLETON EXPLOSION-PROOF SWITCH ASSEMBLY 2 Sheets-Sheet 2 Filed June 4, 1954 INVENTOR. fipule'fn Wary;

f E m z 0 United States Patent EXPLOSION-PROOF SWITCH ASSEMBLY Arthur I. Appleton, Northbrook, Ill.

Application June 4, 1954, Serial No. 434,55t

10 Claims. (Cl. 200-172) This invention relates in general to explosion-proof switch assemblies and, more particularly, to such switch assemblies especially, although not exclusively, suited for use in hospital operating rooms or the like.

It is the general aim of the invention to provide an improved explosion-proof switch assembly which is relatively simple in construction, yet susceptible of convenient recessed mounting as well as easy manipulation as regards closing and opening of the switch by parts of the users body other than his hands.

In a more specific sense, it is an object of the invention to provide such a switch assembly including a switchenclosing box and an escutcheon plate with means for mounting the same on opposite sides of wall partitions of various thicknesses. The escutcheon plate while hearing at its edges against the wall, is also supported at its midportion by an adjustable projection extending through the wall opening.

Another object lies in the provision in such a switch assembly of a positive-acting toggle switch enclosed within an explosion-proof housing together with a rotatable shaft extending through the housing and unique means connecting its inner end to flip the switch actuator upon rotation of such shaft.

A further object is to provide, in such a switch, operating handles or levers which are easily worked by contact with a part of the users body other than his hands, for example, his elbows. Such an arrangement finds advantageous employment, for example, in a hospital operating room in which doctors and nurses may not touch any but sterile objects with their hands.

it is still another object to provide an explosion-proof switch assembly in which the escutcheon plate is held in place solely by connection to a recessed switch box, connection from operating handles journaled in the escutcheon plate to the switch within the box being eifected by telescoping means permitting varying spacing of the box and plate to accommodate walls of various thicknesses. In this aspect, provision is also made for rotatably adjusting the escutcheon plate relative to the box to compensate for misalinement in mounting the latter.

Other objects and advantages will become apparent as the following description proceeds, taken in conjunction with the accompanying drawings, in which:

Figure l is a front elevation of a switch assembly embodying the features of the invention and shown as it appears, when mounted, from the inside of a room;

Fig. 2 is a vertical section taken substantially along the line 2-2 in Fig. 1;

Fig. 3 is a horizontal section taken along the offset planes represented substantially by the line 3-3 in Fig. 1;

Fig. 4 is a vertical transverse section of the switch assembly taken substantially along the line 44 in Fig. 3;

Fig. 5 is a front elevation, similar to Fig. 1, illustrating a second embodiment of the invention; and

Fig. 6 is an exploded detail view illustrating a telescop' 2,794,891 Patented June 4, 1957 ing, adjustable drive connection between two parts of the switch assembly shown in Fig. 3.

While the invention has been illustrated and is described in some detail with reference to particular embodiments thereof, there is no intention that it thus be limited to such detail. On the contrary, the intention is to cover here all alterations, modifications and equivalents falling within the spirit and scope of the invention as defined by the appended claims.

Referring now to Figs. 1-4, the exemplary switch here shown as embodying the invention includes a metal housing or box 10 adapted to be mounted in recessed relation behind. the exposed portion of a building wall. Preferably, this box is formed as a heavy, thick-walled casting of sufficient strength to withstand any explosion which might occur within its confines. For leading electrical wires into and out of the box, a plurality of threaded and apertured bosses 10a are adapted to receive either closure plugs 10b or cooperatively threaded electrical conduits 11. The latter are of sufficient strength and rigidity to render the entire switch and conduit system explosion-proof, and their stiifness may be utilized as the sole support of the box 10. In such an arrangement the conduits would be supported by spaced suitable clamps or brackets although, if desired, the box itself may be mounted by means of brackets engaging the inner surface of the wall.

The box 10 is preferably formed in two sections, thus having a closure lid 10c forming one wall of the box and removably secured to the main portion thereof by suitable fasteners such as machine screws 10d. The mating surfaces of the box 10 and closure lid are preferably accurately machined to provide a snug, substantially airtight fit, thereby serving to contain any explosion within the box 10 or at least to cool escaping gases resulting from such an explosion so that an external combustible atmosphere is not ignited.

For mounting one or more electrical switches 12 within the box 10, an inner casing 14, formed as an open ended rectangular box, is removably secured to the inner face of the lid 10c by suitable fastening means such as machine screws 14a. The inner casing 14 contains a cross plate 15 suitably apertured for mounting the switches 12, the latter being held in place by means of conventional lock nuts 16. The casing 14 also has a pair of openings 18 in its rear wall through which electrical wires connected with the switches 12 may pass into the box 10 and thence through the conduits 11. Preferably the wires are sealed in the apertures 18 by a quantity of plastic or resinous material 19 which, for example, may be a thermosetting plastic rendering the casing 14 substantially airtight. As a result of this construction, the switches 12 are doubly enclosed, rendering their contacts doubly isolated from the outside atmosphere to prevent the escape of hot explosion gases in the event that a spark across the contacts ignites combustible gas which has seeped into the inner casing 14.

In a manner to be more fully described, the switches 12 are adapted to be closed and opened by actuating means extending to the inside of the wall and through an escutcheon plate 20.

In the practice of the invention, the switches 12 may be of the positive snap-acting toggle type which are available commercially and noted for their reliability. These switches include toggle levers 12a which face toward the lid 10c and which are flipped vertically to open and close the switch contacts. In order to efiect such switch action from outside the tightly closed box 10, a pair of actuating shafts 21 rotatably extend through the lid 100, in a manner which prevents the escape of hot gases in the event of an internal explosion, and are 3 connccted by unique means at their inner ends for converting rotary motion of the shafts into linear motion for flipping the levers 12a.

As shown in this instance, the explosion-proof in te rity of the box is maintained even though the shafts 21 rotatably extend through the lid 100 by the formation of cooperative threads at 22 on the inner ends of the shafts and in the lid 100. The threads 22 are preferably of small pitch and relatively tight fit. These threads, therefore, leave the interior of the casing 14 substantially air-tight and capable of withstanding relatively high pressures in the event that arcing of the contacts of the switches 12 creates an explosion within the casing. Moreover, the threads present a long, tortuous path from the interior of the casing 14 to the exterior of the lid 100. Some gases under the pressure of an explosion are forced from within the casing to the outside atmosphere; such gases will be cooled to such a low temperature as to be incapable of igniting an explosive external atmosphere. Since the switches 12 are actuated by rotation of the shafts 21 through less than one revolution, the resulting axial displacement of the shafts due to the threads 22 is negligible.

in order to convert limited rotation of the shafts 21 into a toggle actuating motion, radially-extending, bifurcated arms 24 (Fig. 4) are secured at the inner ends of the shafts, as for example by suitable rivets. Radially slidable within and embraced by the bifurcated portions of the arms 24 are a pair of captive toggleflipping members 25 respectively engaged with the toggle arms 120. In this instance, the members 25 are annular in shape, being concentrically disposed around their respective toggle arms and provided with annular grooves receiving the bifurcated portions of the arms 24 to permit relative radial translation of the member 25. As a result, rotation of the shafts 21 swings the members 25 in a substantially straight vertical line to flip the toggle arms 12a up or down, the freedom of members 25 to move within the arms 24 preventing any side thrust on the toggle arms 12a. Since the toggleflipping members 25 engage the side walls of the inner casing 14 to thereby limit the rotational freedom of the shafts 21 to somewhat less than 180 degrees, a slight freedom of the members 25 to shift radially in the arms 24 is sufficient. And because the shafts may only rotate somewhat less than 180 degrees, there is no problem of axial translation of the members 25 or of loss of the shafts by being completely unscrewed from the lid 100.

In accomplishing another important objective of the invention, means are provided for mounting the escutcheon plate solely by connection with the box 10, and with adjustable spacing therefrom so as to accommodate walls of different thicknesses. Such means include a projection extending from the lid 10c and adapted to receive a fastener inserted through the plate 20, together with an abutment member adjustable axially of the projection. Regardless of the thickness of the wall where the switch is mounted, therefore, the abutment member may be positioned so as to engage the underside of the escutcheon plate and lend support thereto when the fastener draws the edges of the plate against the wall.

As here shown, such a mounting arrangement includes a boss 28 formed integrally or welded on the lid 10c in a central location to project through an Opening in the mounting wall. For purposes of illustration, the inner partition of a double wall is shown in Fig. 3. the wall partition comprising an inner layer of tile 29, a furring layer 30, and a support partition 31. The opposite wall partition may be similarly formed, and the box 1%} disposed within the cavity defined between the two spaced partitions. For mounting the switch assembly, the tile layer 29 is provided with an opening 29a, while a slightly larger recessed opening 32 is cut in the furring 30 and partition 31. As shown, therefore, the

box 10, which is supported principally by the conduits 11, extends into the opening 32, while the boss 28 projects through the opening 29a to receive the escutcheon plate 20. For this latter purpose, the boss 28 is centrally drilled and tapped at 28a, and is externally threaded to receive an axially adjustable abutment sleeve 34 which is threaded internally. The escutcheon plate 20 has a central inwardly flared opening 20a for receiving the head of a fastener screw 35 which extends into threaded engagement with the tapped opening 280. Tightening of the screw 35 brings the edges of the escutcheon plate into firm engagement with the surface of the tile 29, but in order to prevent buckling of the relatively thin plate 20, the sleeve 34 is screwed axially on the stud 28 until its outer end is in abutment with the underside of the plate when the screw 35 has been adequately tightened. By this arrangement, the center portion of the plate 20 is given positive support regardless of the spacing between the box 10 and the escutcheon plate 20 by virtue of adjustments of the sleeve 34 effected by screwing it axially on the stud 28 prior to fastening the plate in place. Therefore, it is not necessary to employ any fastening means whatever between the plate 20 and the wall tile 29. Mounting of the plate 20 is achieved with only one fastening screw 35, and buckling of the plate 20 is prevented by the abutment sleeve 34 which may be adjusted to provide, within limits, any desired spacing between the box 10 and the plate.

In the practice of another feature of the invention, means supported by the escutcheon plate 20 are provided for rotating the shafts 21 to open and close the switches 12, such means being operable by a part of the users body other than his hands and connected with the shafts 21 in a manner to accommodate variations in the spacing between the box 10 and the escutcheon plate 20. For this purpose, a pair of operating handles 40 are journaled in the escutcheon plate 20 and provided with a telescoping connection to the respective shafts 21. As shown in the drawings, the handles 40 include very wide ears or tabs 40a which may be easily engaged by the users elbow, for example, to rotate them and to actuate the switches without employing the hands or other sterile parts of the body. The handles may take various forms in order to permit such actuation but, in any event, will have a relatively large lever portion which is readily engageable by the elbow, arm, shoulder, or other part of the operators body.

For mounting these handles, they are socketed over and locked, as by set screws, on a pair of stems 41 which rotatably extend through the escutcheon plate 20 and are adapted for telescopic, driving connection with the respective shafts 21. As here shown in Figs. 3 and 6, the stems 41 mount at their inner ends transverse pins 41a. The latter may have a press-fit in suitably drilled holes in the stems, and preferably extend transversely from both sides of the stems. The pins 4111 are adapted to socket with driving engagement in diametrically opposite, longitudinal slots 42 cut in the outer ends of the shafts 21, which are cooperatively recessed or drilled at 21a to telescopically receive the stems. It will be perceived that the stems 41 may slide axially within the shafts 21, and the pins within the slots 42, as the escutcheon plate 20 is spaced at different distances from the box 10 in order to accommodate wall panels 29 of different thicknesses. The rotational driving engagement between the handles 40 and i the shafts 21 is thus complete for any wall thickness adjustment within the design limits of a particular switch.

It is to be noted that the escutcheon plate 20 is mounted solely by virtue of its connection with the fastener screw 35 and its abutment with the sleeve 34, as well as its engagement with the two stems 41. It may often happen that the box 10, which is recessed behind the outer surface of the wall, is skewed somewhat with respect to the horizontal and with respect to indicia on the wall, for example, the lines between adjacent blocks of tile. If the escutcheon plate 20 were rigidly fixed in position relative to the box 10, it might therefore be skewed with respect to the horizontal or oth'ei' indicia on the wall and present an unpleasing appearance.

In the present invention, stichdiificnlty is overcome by cooperation between the single fastener screw 35 located in the central areafof the escutcheon platef2'0 and the manner in which the stems 41 are journaled, that is rotatably mounted, in the escutcheon plate. In accordance with the invention, the pins 41 are very loosely journaled within the escutcheon plate on oversized holes and have freedom to shift laterally in such holes when the plate is rotatably adjusted about the fastener 'screw 35. As here shown, the stems 41 are inserted through oversize holes 44 (see Fig. 3) in the escutcheon plate 20 and secured against axial movement relative to the plate by means of washers 45. With the stems 41 thus free to shift relative to the plate 20, the latter may be rotated relative to the box 10 simply by first loosening the screw 35. The escutcheon plate may by this means he accurately alined with indicia on the inner surface of the wall even in the event that the main switch box 10, supported by the conduits 11, is somewhat skewed within its recessed position.

Referring now to Fig. 5, a second embodiment of the invention is there illustrated which is substantially identical with the embodiment described with reference to the other figures, with the exception that only one switch and only one operating handle 40 are employed. While the first described embodiment employs dual switches 12, the embodiment shown in Fig. 5 has only one switch and one operating handle 40 but is otherwise similarly constructed and enjoys all of the advantages set forth above.

I claim:

1. A recessed-mount explosion-proof electrical switch assembly for use in hospital operating rooms and the like comprising, in combination, a closed metal switch box, a switch having a toggle actuator disposed in said box, a shaft rotatably extending through one wall of said box, means for effecting an eccentric connection between said shaft and actuator for moving the latter linearly upon rotation of the former, a centrally drilled and tapped stud projecting outwardly from said one wall and having external threads, an internally threaded sleeve disposed in axially adjustable relation on said stud, an escutcheon plate having an opening therein for receiving a fastening screw threaded into said stud for drawing the plate into abutment with said sleeve, and a wide-cared handle mounted on a stem journaled in said plate and non-rotatably, telescopically connected with said shaft, said handle thereby being rotatable by use of the operators elbow or arm to close or open said switch.

2. An explosion-proof electrical switch assembly susceptible of recessed mounting in the wall of a hospital operating room or the like comprising, in combination, a

metal box having a closure lid defining one wall, a switch having a toggle actuator disposed in said box, a shaft snugly threaded through and rotatable in said lid, a radial arm on the inner end of said shaft, means radially movable in said arm for flipping said toggle actuator upon rotation of said shaft, a centrally drilled and tapped stud projecting outward-1y from said lid and threaded on its external surface, an internally threaded sleeve screwed on said stud and adjustable axially of the latter, an escutcheon plate having an opening therein adapted to register with the central portion of said stud, a single screw inserted through said opening and engaged with said stud for drawing said escutcheon plate into abutment with said sleeve, a stem extending through an oversize opening defined in said escutcheon plate and rotatable and transversely shiftable therein, means adapting said stem and shaft for axially adjustable socketed engagement with said shaft, and a wide-cared handle on the outer end of said stem susceptible of rotational movement by an operators elbow or the like to thereby open and close said switch.

3. An explosion-proof switch comprising, in combina- 6 tion, a closed metal switch box, a switch disposed in said box, a shaft rotatably extending through one wall of said box, means on the inner end of said shaft for actuating said switch upon rotation of the shaft, an external projection on said one wall of said box, an abutment member adjustable along said projection, an escutcheon plate, fastening means engaged between said projection and plate for drawing the latter into engagement with said abutment member, a stem extending through and axially fixed in an oversize opening defined in said plate, a handle on the outer end of said stern for rotating the same, and means affording telescoping, driving connection between said stem and shaft for actuating said switch when said handle is turned, yet permitting variations in the spacing between said box and escutcheon plate.

4. An explosion-proof electrical switch assembly susceptible of recessed mounting behind walls of various thicknesses comprising, in combination, a metal box, a toggle switch mounted within said box, a shaft rotatably extending through one wall of said box andhaving an eccentric connection with the actuator of said switch, an escutcheon plate, a stem rotatably extending through said plate and adapted at its inner end for telescoping driving engagement with said shaft, handle means on the outer end of said stem, and means for securing said escutcheon plate in adjustably spaced relation to said box, said lastnamed means including a projection extending outwardly from said one wall, an abutment member adjustable axially of said projection, and fastening means cngageable between said projection and said plate to draw the latter into abutting relation with said member.

5. In an explosion-proof switch assembly, the combination of a closed metal box, an electric switch in said box, a shaft extending through said box and having means on its outer end for rotating the shaft and means on its inner end for actuating said switch upon such rotation, an escutcheon plate, a tapped and threaded boss on the exterior of said box, an abutment member adjustable along said boss, and fastening means engaged between said boss and plate for drawing the latter into engagement with said abutment member, the spacing between said box and plate being variable by adjustment of said abutment member.

6. In an explosion-proof switch assembly, the combination comprising a closed metal box, a switch in said box, a shaft rotatably extending through said box, means on the inner end of said shaft for actuating said switch upon rotation of the shaft, an escutcheon plate, means for mounting said plate in adjustably spaced relation to said box, a stem rotatably but axially fixed in said plate, and cooperating telescopically locking means on said shaft and stem drivingly connecting the same with freedom permitting adjustment of the spacing between said box and plate.

7. In an explosion-proof switch assembly, the combination of a metal box mountable in recessed relation behind a wall, a switch in said box, a shaft rotatably extending through said box and located to extend through an opening in the wall, means connecting the inner end of said shaft to actuate said switch upon rotation of the shaft, an escutcheon plate, means for mounting the escutcheon plate in spaced relation from said box, a stem rotatably extending through said plate and having freedom to shift transversely but not axially of the plate, means adapting the inner end of said stem to have telescopic connection with said shaft, and means on the outer end of said stem for rotating the same to actuate said switch, the freedom of said stem to shift transversely relative to said plate permitting alinement adjustments of the latter relative to said box.

8. In an electric switch assembly, the combination with a box having a switch therein and a switch-actuating shaft rotatably extending therethrough, of an escutcheon plate, means for securing said plate in adjustable spaced relation to said box, a stem having means for socketing engagement with said shaft, said stem rotatably extending through an oversize opening defined in said plate with freedom for limited transverse movement relative to the latter, and means for preventing axial movement of said stem relative to said shaft, whereby said plate may be shifted relative to said box to compensate for misalinement of the box relative to a mounting wall.

9. In an explosion-proof switch assembly, the combination comprising a closed metal box, a switch in said box, a shaft rotatably extending through said box, means on the inner end of said shaft for actuating said switch upon rotation of the shaft, an escutcheon plate, means for mounting said plate in 'adjustably spaced relation to said box, a stem rotatable but axially fixed in said plate, a transverse pin mounted on the inner end of said stem,

said shaft being formed with a longitudinal recess to 1) telescopically receive said stem and with a longitudinal slot to telescopically receive said pin, whereby said pin maintains rotational driving connection of said stem and shaft as the latter are telescoped to varying degrees according to the spacing adjustment between said box and plate.

10. The combination set forth in claim 9 further characterized in that said shaft is rotatably extended through said box by having a fine pitch threaded engagement with the latter, to thereby provide a tortuous path preventing the escape of hot gases from within said box and produce insignificant axial translation of the shaft relative to the box as the shaft is rotated.

References Cited in the file of this patent UNITED STATES PATENTS 2,240,922 Bissell May 6, 1941 2,287,650 Tornblom June 23, 1942 FOREIGN PATENTS 703,335 France Apr. 28, 1931 

